questions about programming styles

[Bjoern Schliessmann]

fdu.xiaojf at gmail.com wrote:

> Hi all, I'm not skilled at programming, so sorry for my ignorance.

?!

Seems you met many not-so-nice programmers.

> (1)
> which is the better way to calculate the value of attributes of a
> class ? for example:
> 
>  (A)
>     def cal_attr(self, args):
>         #do some calculations
>         self.attr = calculated_value
> and then if the vlue of attribute is needed,
>     self.cal_attr(args)
>     some_var = self.attr
> or I can define cal_attr() as follows:
>  (B)
>     def cal_attr(self, args):
>         #do some calculations
>         return calculated_value
> and then, if the value of attribute is needed,
>     self.attr = self.cal_attr(args)
>     some_var = self.attr

Do you mean when to save a class attribute to an instance or how to
calculate and save something _inside_ an instance? No matter what,
it depends largely on your design. If some value is a
permanent "feature" of an instance, it makes sense to save it as a
member. If the value must always be calculated on the fly, it makes
sense to use a function that returns it. Also check the docs on
Python's "property" feature.
 
> (2)
> when to use class methods and when to use functions ?

Functions are best used if you just "do" something that isn't
focused on a specific class or object type.

Class methods are best used if there is something to "do" that
always needs the class object.
 
> In my opinion, both of class methods and functions have advantages
> and disadvantages. I have to pass many arguments to a function,
> which is annoying. 

Yep. But there are also recipes to let functions store and reuse
parameters, I think.

> When using class methods, the arguments can be stored as
> attributes of the class, which is convenient for later use. But I
> have to create an object in advance. 

But only a class object, which exists when you have defined a class.
Class methods don't operate on instances.

All you asked depends much on specific design. So if you provide
some details, I'm sure at least one here will have a hint.

Regards,


Björn
 
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